Some signal processing applications dealing with sinusoidal signals require that the frequency of these signals be multiplied by an integer. Although methods for frequency multiplication are well-known, frequency multipliers generally suffer from a phase shift inherent in the frequency multiplication process. Proper design of the frequency multiplier will reduce the noise components of this shift to a level which is much less than the maximum tolerable noise. Some of the phase-shift introduced by a frequency multiplier is, however, static in nature, caused by the changing properties of its electronic components. These properties change very slowly with aging, temperature variations and cycling, and the like.
Perhaps the most obvious method of dealing with this unwanted static phase shift is to provide a manually adjusted phase shifter following the output of the frequency multiplier. This approach to static phase shift stabilization, requiring the intervention of a human being, can be accomplished only relatively infrequently. Furthermore, because they are not done continually, such a compensation scheme can allow a significant phase error to accumulate in the output signal between corrections.
As shown in the preceding discussion, there is a need for an apparatus capable of continually correcting static phase shifts such as those introduced by slow changes in the electronic components of the frequency multiplication system, as well as a frequency multiplier which incorporates such phase-shift stabilization capabilities.